The present invention relates to methods and systems for surveillance and guidance of vehicles; more particularly, but not exclusively, the invention relates to airborne surveillance and guidance avionics equipped on Unmanned Aircraft Systems (UAS) for midair collision avoidance and interception.
To integrate UAS into the National Airspace System (NAS), the Federal Aviation Administration (FAA) requires an equivalent level of safety, comparable to see-and-avoid requirements for manned aircraft. UAS must be able to avoid colliding with air traffic or other obstacles that pose a collision hazard, as well as comply with FAA regulations and procedures.
Conventional collision avoidance systems for manned aircraft such as Traffic Collision Avoidance System (TCAS) are unsatisfactory for UAS, mainly because of the lack of autonomous mode of operation and the inability to detect non-cooperative obstacles that do not reply to interrogations, such as vehicles not equipped with transponders, military aircraft equipped with Identification Friend or Foe (IFF) systems operating in Mode 4, and aircraft operating with an interference limited or disabled transponder. TCAS is an important consideration for air traffic safety, as cooperative aircraft equipped with TCAS are required by aviation authorities to comply with Resolution Advisories (RA) provided by the system.
U.S. Pat. Nos. 6,459,411, 6,483,454, 6,657,578 and 6,789,016 suggest using transponder and transceiver equipment such as TCAS, Automatic Dependent Surveillance—Broadcast (ADSB), Station Keeping Equipment (SKE), other types of data links or a combination thereof, to perform both collision avoidance and station keeping (e.g., formation flight) with cooperative aircraft. ADS-B is viewed by the FAA as the key enabling technology for the future air traffic management system. It provides situational awareness as the ADS-B transceiver reports position, velocity and intended trajectory of neighboring vehicles by receiving data from other ADS-B equipped vehicles or from Ground Based Transceivers (GBT) broadcasting Traffic Information System (TIS) messages. ADS-B allows non-cooperative vehicles to be located, as GBT can relay ground-based radar information in TIS broadcasts. SKE is typically used by military aircraft to communicate position, range and control information between formation members for functions such as autopilot. SKE is integrated with TCAS to network surveillance information over the SKE communication links. These inventions have limited capabilities of detecting non-cooperative obstacles through the use of ADS-B, and TIS availability is constrained by ground-based radar and GBT station coverage.
Methods that have been proposed to address these problems include the use of forward-facing cameras mounted on the aircraft, as shown in U.S. Pat. Nos. 4,918,442, 5,581,250 and 7,061,401. These systems are impeded by glare, clutter and artifacts, display intolerance to highly dynamic environments, are unable to accurately determine the range and velocity of neighboring obstacles, and are usually limited to airspace monitored directly in front of the aircraft.
The systems disclosed in U.S. Pat. Nos. 4,755,818, 5,321,489 and 6,804,607 utilize laser beam technology or a combination of laser and camera technology. These inventions exhibit drawbacks similar to camera systems, except for a possible improvement in range determination.
Airborne or ground-based radars are proposed in U.S. Pat. Nos. 3,434,141, 5,050,818, 5,464,174 and 5,872,526 to alleviate some of those issues and offer accuracy suitable for the interception of targets. The significant power requirements of current radars limit the detection range in airborne applications, and reliance on ground-based radars is limited to geographical regions where fixed and mobile radars are or can be deployed.
A combination of TCAS and airborne radar is described in U.S. Pat. No. 6,208,284 and is a suitable method to satisfy the minimum requirements for collision avoidance of both cooperative and non-cooperative obstacles in any type of environment, and allows elegant handling of TCAS Resolution Advisories (RA). This invention allows for the use of TCAS RA but, besides limited range for detecting non-cooperative obstacles, the system cannot avoid terrain, operational airspace boundaries or severe weather.
U.S. Pat. Nos. 4,924,401, 5,136,512 and 5,892,462 propose several methods for performing ground collision avoidance using Above Ground Level (AGL) and Mean Sea Level (MSL) altitude sensors, Digital Terrain Elevation Database (DTED) information and operational airspace restrictions such as a minimum altitude. These inventions cannot avoid small obstacles of high elevation such as communication towers or power lines and do not accommodate for station keeping or interception modes of operation.
The systems described in U.S. Pat. Nos. 6,531,978, 6,785,610 and 7,024,309 offer improved operational capabilities and flexibility by relying on multiple data links and surveillance sensors. None of these methods, however, single-handedly manages all required modes of operation (i.e., collision avoidance, station keeping and interception of targets, takeoff, landing and taxiing of the aircraft) or allows the safe integration of UAS into the National Airspace System (NAS) as these inventions lack compliance with air traffic regulations and procedures.
There is an unmet need for a surveillance and guidance system capable of self-separation, collision avoidance or interception, in all visibility conditions or in the event of sensor or communication failure, while complying with traffic regulations and procedures. Furthermore, there exists a need for such a system that is compact and lightweight, and which optimizes the employment of its navigation, communication and surveillance systems so as to maximize efficiency and minimize power requirements and cost. It is also desirable for the system to be capable of operating regardless of the command and control system or of the interface available on the vehicle, without the need for user input and in different airspace environments.